Meaning and etiopathogenesis of sectorial transient hepatic attenuation differences (THAD)

Purpose. To examine sectoral transient hepatic attenuation differences (THAD) in an attempt to correlate semeiotics with etiopathogenesis and to deduce a possible diagnostic value. Materials and methods. Over a period of three years (January 1998-January 2001) we observed 130 THAD in 988 patients, and we selected 30 sectoral THAD in 18 patients (10 males and 8 females), ranging in age from 24 to 82 years (average = 63.3). The 18 patients comprised 6 cancer patients undergoing CT staging/restaging, 5 cirrhotic patients being studied for possible hepatocellular carcinoma, 7 patients undergoing helical CT to further investigate clinical and/or US findings. For each patient a biphasic helical CT liver examination was performed, during the arterial and portal dominant phase. After the first diagnosis, all patients were followed up for 12 months with at least one US and helical CT examination; 8/18 were also studied by MRI . Results. Thirty THAD were associated with 14 metastatic lesions, 4 hepatocellular carcinomas, 1 cholangiocarcinoma of the liver, 4 haemangiomas, 3 abscesses, 1 FNH, 2 cases of arterioportal shunting (APS) and 1 fine-needle percutaneous biopsy. Nine THAD turned out to be the sole sign of disease and occurred at least 3/6 months before the causal focal lesion had become detectable. At the first examination, all focal lesions had a maximum diameter of 2 cm; the size of THAD varied from 1 to 5 cm. All of the THAD were sectoral, with the base side represented by the glissonian capsule and the apex towards the parenchyma. 27/30 THAD were connected to focal lesions: 24/27 were fanshaped and the lesion was situated at the apex of the triangle; 3/27 were roughly wedge-shaped and the lesion was entirely inscribed in the hyperattenuating area. 3/30 were not connected to focal lesions, being in 2 cases fan-shaped and in only one case irregularly shaped. Conclusions. Sectoral THAD may or may not be connected to focal lesions. Whenever a sectoral THAD not connected to a focal lesion is detected, all of the possible causes should be considered: portal or superhepatic vein thrombosis, traumatic (biopsy) or cirrhotic intraparenchymal APS, or a benign occult nodule. If none of these explanations are confirmed, we should consider the possibility of an occult malignant lesion.